[llvm] [RFC][DataLayout] Add null pointer value infrastructure (PR #183207)

[Alexander Richardson via llvm-commits]

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@@ -756,9 +800,21 @@ void DataLayout::setPointerSpec(uint32_t AddrSpace, uint32_t BitWidth,
     I->HasUnstableRepresentation = HasUnstableRepr;
     I->HasExternalState = HasExternalState;
     I->AddrSpaceName = AddrSpaceName.str();
+    I->NullPtrValue = std::move(NullPtrValue);
   }
 }
 
+APInt DataLayout::getNullPtrValue(unsigned AS) const {
+  auto I = lower_bound(PointerSpecs, AS, LessPointerAddrSpace());
+  if (I != PointerSpecs.end() && I->AddrSpace == AS && I->NullPtrValue)
+    return *I->NullPtrValue;
+
+  unsigned BitWidth = getPointerSizeInBits(AS);
+  if (DefaultNullPtrValue->isZero())
+    return APInt::getZero(BitWidth);
+  return APInt::getAllOnes(BitWidth);
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arichardson wrote:

Would it make sense to change this to sign-extend? Doesn't really make it much shorter though.

https://github.com/llvm/llvm-project/pull/183207